Time-resolved X-ray Diffraction Analysis Research Articles

Bioactive glass–ceramics containing fluorapatite, xonotlite, cuspidine and wollastonite form apatite faster than their corresponding glasses

Crystallisation of bioactive glasses has been claimed to negatively affect the ion release from bioactive glasses. Here, we compare ion release and mineralisation in Tris–HCl buffer solution for a series of glass–ceramics and their parent glasses in the system SiO2–CaO–P2O5–CaF2. Time-resolved X-ray diffraction analysis of glass–ceramic degradation, including quantification of crystal fractions by full pattern refinement, show that the glass–ceramics precipitated apatite faster than the corresponding glasses, in agreement with faster ion release from the glass–ceramics. Imaging by transmission electron microscopy and X-ray nano-computed tomography suggest that this accelerated degradation may be caused by the presence of nano-sized channels along the internal crystal/glassy matrix interfaces. In addition, the presence of crystalline fluorapatite in the glass–ceramics facilitated apatite nucleation and crystallisation during immersion. These results suggest that the popular view of bioactive glass crystallisation being a disadvantage for degradation, apatite formation and, subsequently, bioactivity may depend on the actual system study and, thus, has to be reconsidered.

Synthesis, structure and properties of MAB phase MoAlB ceramics produced by combination of SHS and HP techniques

The kinetics and stages of phase formation in the combustion wave of the MoAlB mixture are studied. The phase diagrams in the Mo-Al-B system were built using the AFLOW and Materials Project databases. The time-resolved X-ray diffraction analysis demonstrate that the MoAlB phase crystallizes from the melt without formation of any intermediate compounds. The structure of the synthesized ceramics was MoAlB lamellar grains 0.4 µm thick and ~2–10 µm long. Compact samples characterized by homogeneous structure and low residual porosity were obtained by hot pressing of SHS powders. The ceramic MoAlB has a layered structure, which is consistent with the morphology of the synthesis products. Mechanical and thermophysical properties are measured for samples obtained under optimal HP conditions at 1300 °C. The calculated value of the oxidation rate for MoAlB at 1200 °C for 30 h was 2.21∙10−5 mg/(cm2∙s). Oxide layer ~14 µm thick consists of elongated polygonal Al2O3 grains.

Investigation of the Interaction between Perovskite Films with Moisture via in Situ Electrical Resistance Measurement.

Organometal halide perovskites have recently emerged as outstanding semiconductors for solid-state optoelectronic devices. Their sensitivity to moisture is one of the biggest barriers to commercialization. In order to identify the effect of moisture in the degradation process, here we combined the in situ electrical resistance measurement with time-resolved X-ray diffraction analysis to investigate the interaction of CH3NH3PbI(3-x)Cl(x) perovskite films with moisture. Upon short-time exposure, the resistance of the perovskite films decreased and it could be fully recovered, which were ascribed to a mere chemisorption of water molecules, followed by the reversible hydration into CH3NH3PbI(3-x)Cl(x)·H2O. Upon long-time exposure, however, the resistance became irreversible due to the decomposition into PbI2. The results demonstrated the formation of monohydrated intermediate phase when the perovskites interacted with moisture. The role of moisture in accelerating the thermal degradation at 85 °C was also demonstrated. Furthermore, our study suggested that the perovskite films with fewer defects may be more inherently resistant to moisture.

Growth of aligned multi-walled carbon nanotubes: First in situ and time-resolved X-ray diffraction analysis

Catalytic chemical vapour deposition has become a method of choice to produce carbon nanotubes (CNT), particularly for the synthesis of aligned nanotube forests. But a thorough understanding of the mechanisms for CNT nucleation, growth and alignment is still missing. In situ and time resolved experiments allowing to study these processes in real conditions are required. We have developed a specific reactor and furnace to perform such experiments using X-ray diffraction (XRD). Experiments were performed at synchrotron SOLEIL. XRD patterns were recorded as a function of time, during nucleation and growth. We present here our first results, discussing the interest of the XRD method with respect to other existing in situ methods.

Time-resolved X-ray diffraction analysis of the experimental dehydration of serpentine at high pressure

Time-resolved, in situ X-ray diffraction analysis was used to determine the dehydration rate and kinetics of serpentine during experimental dehydration at high pressures. The capsule used comprises a diamond sleeve fitted with Au or Pt lids in order to provide high-quality, time-resolved X-ray diffraction data. Antigorite quickly dehydrated to enstatite + forsterite + fluid within 2 h at 650 °C below ∼ 6 GPa. Avrami modeling of the results and SEM observations of the partially dehydrated sample revealed that the nucleation rate was quite high for enstatite but low for forsterite, showing incubation periods of ∼ 10 min before appearing. The crystallization of these minerals is controlled largely by the composition of the fluid generated from serpentine dehydration. The dehydration boundary determined below 6 GPa in the present study is consistent with the results of previous phase equilibrium studies. This study indicates that serpentine in a subducting slab dehydrates rapidly below 6 GPa when the slab intersects the dehydration boundary conditions.

Continuous time-resolved X-ray diffraction of the biocatalyzed reduction of Mn oxide

Here we report the first continuous time-resolved X-ray diffraction analysis of a biologically mediated mineral reaction. We incubated total membrane (TM) fractions of the facultative anaerobe Shewanella oneidensis in an anoxic environmental reaction cell with formate (as electron donor via formate dehydrogenase) and powdered birnessite, a layered Mn 3+ , 4+ oxide common to many soils. Using both synchrotron and conventional X-ray sources, we irradiated the reaction mixtures for up to two weeks and observed bioreduction and dissolution of birnessite and the concomitant precipitation of rhodochrosite [Mn 2+ CO 3 ] and hausmannite [Mn 2+ Mn 2 3+ O 4 ]. The high time resolution of these experiments documented systematic changes in crystal structure during the breakdown of birnessite and the emergence of nanocarystalline rhodochrosite. In addition, the relative abundances of birnessite and rhodochrosite were quantified over time for different concentrations of TM fraction, allowing for the determination of rate equations that govern this bioreaction. Importantly, constant irradiation for two weeks did not stop the enzymatic reaction, suggesting that enzymes may be more resilient than whole cells when exposed to X-ray radiation.

Development of in-Situ Microstructure Observation Techniques in Welding

Unidirectional solidification for low-carbon steel weld metal was characterized by the using Time-Resolved X-Ray Diffraction (TRXRD) system. Solid-state phase transformation was also observed in situ in reciprocal lattice space. It was shown that TRXRD analysis has a potential as a comprehensive characterization technique for solidification and phase transformation processes in welding. Furthermore, it was suggested that nucleation sites in solid-state phase transformation can be observed by high-temperature laser scanning confocal microscopy (HLSCM) in order to classify the ferrite microstructure. These techniques have been designed for the dendrite alignment in unidirectional solidification and the δ-β-α phase transformation in steel weld metal to be characterized.

Influence of the Crystalline State on Photoinduced Dynamics of Photoactive Yellow Protein Studied by Ultraviolet-Visible Transient Absorption Spectroscopy

Time-resolved ultraviolet-visible spectroscopy was used to characterize the photocycle transitions in single crystals of wild-type and the E-46Q mutant of photoactive yellow protein (PYP) with microsecond time resolution. The results were compared with the results of similar measurements on aqueous solutions of these two variants of PYP, with and without the components present in the mother liquor of crystals. The experimental data were analyzed with global and target analysis. Distinct differences in the reaction path of a PYP molecule are observed between these conditions when it progresses through its photocycle. In the crystalline state i), much faster relaxation of the late blue-shifted photocycle intermediate back to the ground state is observed; ii), this intermediate in crystalline PYP absorbs at 380 nm, rather than at 350–360 nm in solution; and iii), for various intermediates of this photocycle the forward reaction through the photocycle directly competes with a branching reaction that leads directly to the ground state. Significantly, with these altered characteristics, the spectroscopic data on PYP are fully consistent with the structural data obtained for this photoreceptor protein with time-resolved x-ray diffraction analysis, particularly for wild-type PYP.

In situ measurement of high-temperature thermal diffusivity in a combustion-synthesized ceramic

A simple method to calculate thermal diffusivity in situ after a combustion synthesis reaction is presented. The combustion reaction was analyzed via time-resolved X-ray diffraction analysis and infrared thermography. Thermal diffusivity was estimated and used to calculate temperature profiles based on temperature profiles one second earlier. For a sample of TiC formed from Ti and C, a value of 2.00×10-6±0.20×10-6 m2 s-1 was calculated for temperatures between 1000 and 1900 K. This method is rapid and can avoid some problems associated with furnace-based measurements of thermal diffusivity, such as recrystallization and destruction of non-equilibrium phases.

Investigation of Time-Resolved X-Ray Diffraction Analysis in Smectic A Liquid Crystal Cells

Time-resolved X-ray diffraction analysis of smectic A liquid crystal cells is investigated. Frequency and duty ratio dependence of smectic A layer motions is measured. From the experimental results, possible mechanisms of layer motions are discussed.